This invention relates to a method of manufacturing a semiconductor device and to such a device, for example a semiconductor laser device.
EP-A-166593 describes a semiconductor device having a waveguide structure, for example a semiconductor laser device, where the device is formed by growing a first doped region as a superlattice region comprising alternate layers of a first and a second semiconductor material on a semiconductor device substrate. A waveguide region is grown comprising at least a superlattice region comprising alternate layers of the first and second semiconductor materials on the first doped region, and a second doped region is grown as a superlattice comprising alternate layers of the first and second semiconductor materials on the waveguide region.
As described in EP-A-166593, the waveguide region comprises first and second superlattice regions bounding a quantum well region forming the active region of the, for example, laser device and the first and second doped regions are oppositely doped to form a diode struture for enabling carriers to be injected into the active region when a forward biasing voltage is applied across the device.
The first and second materials used to form the superlattice regions of the device described in EP-A-166593 are binary compounds, for example gallium arsenide (GaAs) and aluminum arsenide (AlAs), and in order to enable the waveguide region to act as a confinement region for the active region the relative thicknesses of the first and second material layers are different in the first and second superlattice regions of the waveguide region from the relative thicknesses of the first and second material layers in the first and second doped regions. In particular, where the first and second material layers are formed of aluminum arsenide and gallum arsenide then the thickness of the gallum arsenide layers is increased in the first and second superlattice regions of the waveguide region so that the fraction or percentage of aluminum is less in the waveguide region than in the first and second doped regions and so the waveguide region has a smaller effective bandgap and higher refractive index than the first and second doped regions, enabling the waveguide region to function in operation of the device as a waveguide for light generated in the active region and as a confinement region for injected carriers.